Research has shown that teachers' autonomy support and provision of structure relate to students' agentic and behavioral engagement. Moreover, agentic engagement elicits higher teacher autonomy support. In the present 5-week diary study, we investigated the dynamic nature of this interplay between teachers and students through their cross-assessment of students' agentic and behavioral engagement. We also considered the week-to-week student-reported teacher autonomy support and provision of structure as well as two student personal characteristics -- proactive personality and situational autonomous versus controlled motivation. Two hundred fifty-seven Turkish middle school students and their teachers from 13 classes participated in the study. Multilevel analyses showed that students' week-to-week perceived autonomy support and initial level of autonomous motivation positively predicted week-to-week agentic engagement (teacher- and student-reported). Students' week-to-week perceived structure positively predicted week-to-week agentic and behavioral engagement (student-, but not teacher-, reported). These findings indicate the interplay between students' situational engagement and teachers' situational motivating style (i.e., autonomy support and provision of structure). They also suggest greater predictive power for students' situational motivation over the personal trait of proactive personality.